If you want the feel of CS 1.5 (old recoil, old movement, no riot shield) but with modern resolution support, download the free mod for Counter-Strike: Global Offensive (CS:GO) or Counter-Strike 2 (CS2) community workshop.
To understand the "CS 15" myth, we have to look at how Counter-Strike titles have been named historically. counter strike 15 cd key new
Because the official servers are dead, playing 1.5 today requires community-made workarounds: WON2 Network If you want the feel of CS 1
Instructions on how to run to access the original CS mod counter strike 15 cd key new