I'm not sure that 2.5 mcg will do all that much, but it would certainly depend on the individual.
I take 5 mcg cytomel daily and have been on it for about a year now, along with levo (T4 med). My FT3 is barely mid range. It has not raised my temp, nor does it seem to affect my pulse or heart rate, although a larger dose did.
Again --- the affect it has will depend on the individual and if you suspect problems, you should contact your doctor.
Like Barb said, that not much cytomel, depends. You must be spliting the 5 mcg?
On the other hand starting this t3 med at minimal dose is a good way to try it, in case someone is sensitive to it. If its not enough, well, no harm done.
Cyto at 10 mcg a day is almost very noticeable to all, starting at 10 can make temporary hyper symptoms at first.
How much T4 is this new T3 being added to?