The presence or absence of a log backup will make absolutely no difference in this case as you're shrinking a data file, not a log file.
LOB data causes shrinks to run slowly, as do heaps with nonclustered indexes on them. If you have lots of either of those then you'll just have to be patient.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability