15/42 is very close to your 16/45 but the RPM is slightly lower on the 15/42.
You are aware that stock is 16/40 and your gearing is much better for slow speed acceleration right? The bigger the rear sprocket, the lower the gear ratio. The previous owner lowered your gear, stock it would be worse.
Stock gearing gives you 77mph at redline in 1st, while your gearing gives 68mph.
At redline in 6th, stock gearing would be 196 and yours would be 174.
If you were willing to accept a top speed of 163, you could go 15/45 and that would be a beast power wise.