S potassium is 5.54 mmol/l. doc prescribed losartan potassium for htn & ckd. will it further increase s. potassium level? isn't telmisartan better?

Yes: Both may increase your potassium. I would try hydrochlorothiazide if it is for blood pressure. This will decrease your potassium. Or, recheck your potassium; it may not be as high as that.

Class effect: Both Losartan and Telmisartan could increase potassium. Perhaps there was a reason the potassium was elevated (if blood sits too long before running the sample for example) so maybe the doctor to that into consideration. I would confirm with your doctor though as he/she may want to repeat the test.