Assalam O Alaikum!
If it is the Alto You are talking about, then yes, There should be some problem.
(a) To improve efficiency, keep the RPM between 2000 - 3000.
(b) Check the Spark Plugs and Replace them is necessary.
(c) Check the Cam Belt. If it is lose, Replace it.
(d) If alloy rims are not same size in width or length, then they will cause problem to axle also.
(e) Check the engine lubricant level.
(f) Tappet adjustment or valve clearance can definitely help.
(g) Are you using A/C? It decreases efficiency and increases load. Are you maintaining it properly?
I personally think that alloy rims is not the issue. It is that the greedy mechanics usually swap or remove some parts is our absence. Try going to an authorized Suzuki Dealer for checkup only. Then decide where to fix car from