Many people report a lower resting heart rate after ablation.
In some cases it is because of new medication (beta-blockers), in other cases there seems to be no apparent reason...
35-40 is quite low, but normally not dangerous as long as you are not dizzy or fainting and as long as it goes up when you are active.
15 days after ablation is still short and it is too soon to speak of a definitive situation.
If you really worry, you could contact the hospital for advice .
Also, you could ask your question in the heart rhythm forum. You will probably get more elaborate answers there.