can we use UPS as stabilizer for 1.5 ton AC?
The key facts about your A/C are

Power Requirements  1/230V/50Hz
Cooling Operating Current   7 A


7 A x 230 V = 1610 Watts. UPS specs are in VA not W due to power-factor corrections which I'll ignore:

Your 800 VA UPS is probably not a good choice for a 1610 W load.