That turbo looks big (Like T4 sized maybe?) if so then this will be why it's laggy.

The general rule is standard exhaust cam and modified inlet (BD14 like you have)

I would say if you don't like the lag then really you should go for a smaller turbo, you won't have as much power, ultimatly, but it will be more responsive lower down.

It's essentially always a compromise between power and lag.

I think M27 relates to a 'casting' number.

Martin