I moved from PTSB,and June will be my first repayment,so it is possible.
I moved due to the very high rates having come out of a five year fixed,and like the OP I had a two prong mortgage,with some of it being on interest only for five years the rest was then back to a very expensive variable rate.
The fixed rate with PTSB was beyond belief!
The only issue I found was trying to get the remainder of the interest only term,ie; been on it for two years and had three left..all mortgage lenders said they would allow this after one year of payments.
Im now on a three year fixed rate with KBC,and on the interest only portion,Im now paying both interest and capital with the option to go back to interest only next year.
Either way the repayments for both are still CHEAPER than the variable rate with PTSB.
I did go to a broker..dont think it would have made much difference really,apart from the fact that the broker was very efficient and they did all the communication between me and the banks..