The hks2535 isn't the most responsive thing on a rb20...in fact...just about any turbo except for the stocker won't be responsive...i know because i've got a 2535 on a rb20...however...yours seems alot worse...
The guys here have basically covered all your bases...restrictions in your system would be first thing...and then after getting the proper support mods a tune will go a long way to improving driveability once you dial some timing in...if you cannot afford engine management and a tune now then suck it up and drive it the way it is...do not run at at 14psi...turn it down to 10psi and run it till you can afford it...mind you it will run like a POS till then...
HKS turbos usually come with an adjustable actuator which you could possibly shorten to bring on slightly better response...mind you max boost will also rise so be careful...and when the time comes for the tune...running higher max boost will also improve boost resposne down low...i have attached my dyno graph from my recent tune...it should give you an idea of what boost response vs rpm you should be expecting...thats at 19psi though so boost response is abit better but its still gutless down low...