535d Turbos barely working

[AdamFor]

Hi all, I know this has been covered several times before but I feel like this symptoms are different on my 535d, it's literally has the same power as my remmaped e90 320d , I took it to the garage last week who after 2 days told me they think its the big turbo that needs replacing, I did ask about vacuum hoses and they said they are all fine but the large turbo has play and is dirty and doenst spin very well from what I could understand, the car literally feels like a naturally aspirated vehicle so like theres no turbo through the whole rev range which makes me think it's not small turbo , the car has been previously remmaped dpf and egr blank , it is a 2005 e60 535d with just short of 120k on clock ( miles ) I'm asking for advice before I take the 1500£ plunge for large turbo, my code reader bought up flow control valve fault which I'm not sure if that has anything to do with it?? Thanks in advance guys.