I cannot install Tensorflow Version 1.15 through pip

You are using python 3.8, which was not officially supported when tensorflow was at version 1.15. You can also check on pypi, there are no files available for cp38, even for 2.10 Onle the versions listed by your command have a cp38 whl file available, see here

Since you have conda, simply create a virtual env with the required version

conda create -n tf python=3.7

then install tensorflow in this env

You must be using python <=3.7 to install Tensorflow 1.15. See the pypi release page. Assuming you are and you still get this issue, upgrading from pip-20.1.1 to pip-21.0.1 fixed it for me. Try upgrading pip.