diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index a3fc064f..d4d95220 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -20,7 +20,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.11', '3.12', '3.13', '3.14']
+        python-version: ['3.11', '3.12', '3.13', '3.14', '3.15']
 
     steps:
     - uses: actions/checkout@v7.0.1
diff --git a/.gitignore b/.gitignore
index 07980c8a..116b3e71 100644
--- a/.gitignore
+++ b/.gitignore
@@ -199,7 +199,7 @@ fabric.properties
 ### Custom ###
 ex.py
 experiments/
-.vscode/tags
+.vscode/
 .pyre
 .pytype
 build/
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a4c613c..14f280a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ Versions before `1.0.0` are `0Ver`-based:
 incremental in minor, bugfixes only are patches.
 See [0Ver](https://0ver.org/).
 
+## 0.30.0 WIP
+
+### Features
+
+- Add `python3.15` support
+
 
 ## 0.29.1 WIP
 
diff --git a/returns/contrib/mypy/_typeops/analtype.py b/returns/contrib/mypy/_typeops/analtype.py
index c6835325..c651f008 100644
--- a/returns/contrib/mypy/_typeops/analtype.py
+++ b/returns/contrib/mypy/_typeops/analtype.py
@@ -1,5 +1,4 @@
 from collections.abc import Sequence
-from types import MappingProxyType
 from typing import Final, Literal, overload
 
 from mypy.checkmember import analyze_member_access
@@ -9,8 +8,9 @@
 
 from returns.contrib.mypy._structures.args import FuncArg
 from returns.contrib.mypy._structures.types import CallableContext
+from returns.primitives.compat import make_immutable
 
-_KIND_MAPPING: Final = MappingProxyType({
+_KIND_MAPPING: Final = make_immutable({
     # We have to replace `ARG_OPT` to `ARG_NAMED`,
     # because `ARG_OPT` is only used in function defs, not calls.
     # And `ARG_NAMED` is the same thing for calls.
diff --git a/returns/contrib/mypy/_typeops/transform_callable.py b/returns/contrib/mypy/_typeops/transform_callable.py
index 059ae652..450cbd57 100644
--- a/returns/contrib/mypy/_typeops/transform_callable.py
+++ b/returns/contrib/mypy/_typeops/transform_callable.py
@@ -1,4 +1,3 @@
-from types import MappingProxyType
 from typing import ClassVar, Final, final
 
 from mypy.nodes import (
@@ -22,6 +21,7 @@
 from mypy.types import Type as MypyType
 
 from returns.contrib.mypy._structures.args import FuncArg
+from returns.primitives.compat import make_immutable
 
 _VARIADIC_KINDS: Final = frozenset((ARG_STAR, ARG_STAR2))
 """Kinds of arguments that consume leftover arguments.
@@ -33,7 +33,7 @@
 _POSITIONAL_KINDS: Final = frozenset((ARG_POS, ARG_OPT))
 """Kinds of arguments that can be passed positionally."""
 
-_KEYWORD_ONLY_KINDS: Final = MappingProxyType({
+_KEYWORD_ONLY_KINDS: Final = make_immutable({
     ARG_POS: ARG_NAMED,
     ARG_OPT: ARG_NAMED_OPT,
 })
diff --git a/returns/contrib/pytest/plugin.py b/returns/contrib/pytest/plugin.py
index f7c4fb9f..cf8413b8 100644
--- a/returns/contrib/pytest/plugin.py
+++ b/returns/contrib/pytest/plugin.py
@@ -1,18 +1,10 @@
 import inspect
 import sys
-from collections.abc import Callable, Generator, Iterator
+from collections.abc import Callable, Generator, Iterator, Mapping
 from contextlib import ExitStack, contextmanager
 from functools import partial, wraps
-from types import FrameType, MappingProxyType
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Final,
-    TypeAlias,
-    TypeVar,
-    Union,
-    final,
-)
+from types import FrameType
+from typing import TYPE_CHECKING, Any, TypeAlias, TypeVar, Union, final
 from unittest import mock
 
 import pytest
@@ -148,7 +140,7 @@ def _spy_error_handling() -> Generator[_ErrorsHandled]:
     errs: _ErrorsHandled = {}
     with ExitStack() as cleanup:
         for container in _containers_to_patch():
-            for method, patch in _ERROR_HANDLING_PATCHERS.items():
+            for method, patch in _error_handling_patchers().items():
                 cleanup.enter_context(
                     mock.patch.object(
                         container,
@@ -182,6 +174,16 @@ def _containers_to_patch() -> list:
     ]
 
 
+def _error_handling_patchers() -> Mapping[str, Callable]:
+    from returns.primitives.compat import make_immutable  # noqa: PLC0415
+
+    return make_immutable({
+        'lash': _patched_error_handler,
+        'map': _patched_error_copier,
+        'alt': _patched_error_copier,
+    })
+
+
 def _patched_error_handler(
     original: _FunctionType,
     errs: _ErrorsHandled,
@@ -224,10 +226,3 @@ def sync_wrapper(self, *args, **kwargs):
         return original_result
 
     return wraps(original)(sync_wrapper)  # type: ignore
-
-
-_ERROR_HANDLING_PATCHERS: Final = MappingProxyType({
-    'lash': _patched_error_handler,
-    'map': _patched_error_copier,
-    'alt': _patched_error_copier,
-})
diff --git a/returns/primitives/compat.py b/returns/primitives/compat.py
new file mode 100644
index 00000000..95bba472
--- /dev/null
+++ b/returns/primitives/compat.py
@@ -0,0 +1,16 @@
+import types
+from collections.abc import Mapping
+from typing import TypeVar
+
+_KT = TypeVar('_KT')
+_VT = TypeVar('_VT')
+
+
+def make_immutable(
+    mutable_dict: Mapping[_KT, _VT],
+) -> Mapping[_KT, _VT]:
+    """Make a dictionary immutable."""
+    try:  # pragma: >=3.15 cover
+        return frozendict(mutable_dict)  # type: ignore[no-any-return, name-defined, unused-ignore]
+    except NameError:  # pragma: <3.15 cover
+        return types.MappingProxyType(mutable_dict)
diff --git a/setup.cfg b/setup.cfg
index ec5a5179..35a1e638 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -54,6 +54,8 @@ per-file-ignores =
   # We allow `futures` to do attribute access:
   returns/future.py: WPS402
   returns/_internal/futures/*.py: WPS204, WPS433, WPS437
+  # Allow `types.MappingProxyType` in compat code:
+  returns/primitives/compat.py: WPS483
   # We allow a lot of durty hacks in our plugins:
   returns/contrib/mypy/*.py: S101, WPS201
   returns/contrib/pytest/__init__.py: F401