Unsatisfactory output of 16 QAM transmitter with RRC filter

I am simulating 16 QAM transmitter(data rate : 128 Kbps) with RRC filter(Root Raised Cosine).My filtered output is not obtained as desired. My model and FDA tool interface are attached. My requirement is to get a good frequency response and constellation. Filter specs I gave are:

Filter order :128

Window :Chebyshev (120 dB stop band attn)

Sampling frequency : 128KHz (modulated data was up sampled 4 times)

Cut off :15.15KHz

I am confused about cut off as I found it is 1/2Ts in many textbooks. Please help me by hinting about discrepancies in my simulation.