The reason it won't go above 15psi is the fact you got blue injectors which simply will not provide sufficent fuel for anymore than 13-14psi. I am suprised you have got 15psi. You will need to run beiges or bigger for more power and at least a stage 2 chip. With the t34 and the rest of your mods outlined with the correct fuelling and good set up should see you easily touch 200bhp mate. You can get a ofac to run over 21psi if you so wish with the correct tuner but you are talking big boost then and defo steel bootm end to safely run this. Another thing you want to consider is driveability. It's all good having 250,270 even 300 hp is possible form the 1.6 but you can't really drive it on the road because as soon as you hit half throttle you will just light up the wheels in any gear.