I've done some more testing and Blast doesn't seem to have helped the issue. After some extensive testing, the issue almost appears to be on the virtual desktop side but only to the printers that are there passed through from ThinPrint. Some jobs take longer time to queue up than others. When the job takes longer, it will show up in the queue as for example at 5.0 MB in size and sit there. Then... shortly after, the size shows as 5.0/5.0 MB and then the job is moved out and transferred to the Thin Client very quickly from there forward. I'm not sure if this helps.
I also did another test by using a full clone VM. I print to the same printer that is appearing via ThinPrint, and it's slow queueing up. If I install that very same printer local inside the full clone, it's very fast. This again shows me that the issue is clearly only when using a printer that is from ThinPrint, are we seeing the issue.
Unfortunately we are stuck on this one at the moment and it's affecting our production work.