Buy a Mitsubhishi 13000 BTU a/c that will save energy atleast 45% than ur window.
Window a/c i have experianced with time consume more electercity and when the electercity is low in high load areas the amp can go upto 15 to 16 which is very high.
Split of 1 ton consumes around 4.5 to 5.5 amp i use to have general a/c in my room 1.5 ton now i am using chinese kenwood 1 ton.
Interms of cooling the general use to work in 5 to 10 mins and my split now takes around 15 mins to cool the room and saving you can calculate. I run it at 28 and i am happy with cooling in day or night.
If you compare split 1.5 ton to old general 1.5 ton still the split consumes less amp as compare to general so for sure it consumes less electercity in running.
Now electercity saving also depends on how soon can your a/c reach the desire temperature and thermostate turns the compressor off and how long can your room hold this cold.
I use to own 2 window a/c, One General which uses the piston type compressor and other one was National with rottery compressor.