It (currently) sounds like 'pitcha' (English) to me. I gather that it should sound more like 'pizza'?
It should sound exactly like "pizza", except spelled the Welsh way as "pitsa".
Unfortunately the TTS can't do this and we're not able to edit the individual sound, we had hoped to turn it off but that doesn't seem to be working at present.
I agree, it uses the [tʃ] sound (initial sound of English cheese, church); i suspect [ts] is the more correct pronunciation.