Install requirements issue

[Vladimir]

Hello!
When I try to install requirement libs using command:
pip3 install -r requirements.txt
I have an error with this output:

Defaulting to user installation because normal site-packages is not writeable
Requirement already satisfied: attrs==19.3.0 in /usr/lib/python3/dist-packages (from -r requirements.txt (line 1)) (19.3.0)
Collecting gym==0.17.1 (from -r requirements.txt (line 2))
  Using cached gym-0.17.1.tar.gz (1.6 MB)
  Preparing metadata (setup.py) ... done
Requirement already satisfied: mpi4py==3.0.3 in /usr/lib/python3/dist-packages (from -r requirements.txt (line 3)) (3.0.3)
Collecting numpy==1.17.3 (from -r requirements.txt (line 4))
  Using cached numpy-1.17.3-cp38-cp38-manylinux1_x86_64.whl (20.5 MB)
Requirement already satisfied: pybullet>=3.0.6 in /usr/local/lib/python3.8/dist-packages (from -r requirements.txt (line 5)) (3.2.5)
ERROR: Ignored the following versions that require a different python version: 1.25.0 Requires-Python >=3.9; 1.25.0rc1 Requires-Python >=3.9; 1.25.1 Requires-Python >=3.9
ERROR: Could not find a version that satisfies the requirement tensorflow==1.15.4 (from versions: 2.2.0, 2.2.1, 2.2.2, 2.2.3, 2.3.0, 2.3.1, 2.3.2, 2.3.3, 2.3.4, 2.4.0, 2.4.1, 2.4.2, 2.4.3, 2.4.4, 2.5.0, 2.5.1, 2.5.2, 2.5.3, 2.6.0rc0, 2.6.0rc1, 2.6.0rc2, 2.6.0, 2.6.1, 2.6.2, 2.6.3, 2.6.4, 2.6.5, 2.7.0rc0, 2.7.0rc1, 2.7.0, 2.7.1, 2.7.2, 2.7.3, 2.7.4, 2.8.0rc0, 2.8.0rc1, 2.8.0, 2.8.1, 2.8.2, 2.8.3, 2.8.4, 2.9.0rc0, 2.9.0rc1, 2.9.0rc2, 2.9.0, 2.9.1, 2.9.2, 2.9.3, 2.10.0rc0, 2.10.0rc1, 2.10.0rc2, 2.10.0rc3, 2.10.0, 2.10.1, 2.11.0rc0, 2.11.0rc1, 2.11.0rc2, 2.11.0, 2.11.1, 2.12.0rc0, 2.12.0rc1, 2.12.0, 2.12.1, 2.13.0rc0, 2.13.0rc1, 2.13.0rc2, 2.13.0)
ERROR: No matching distribution found for tensorflow==1.15.4

My system is:
Ubuntu 20.04
Python 3.8.10