I mostly do my cleanup work on a old Dell running XPpro SP3 P4-3.2 w/2G RAM, so I am used to slow launches

I have 3 custom columns and 4 color rules. I leave ALL the optional windows closed.
I just slurp coffee while the Editor opens; Both Sigil and Calibre's editor take significant (15-30secs) time to open a book. Calibre stomps Sigil on overall operational running speed.
Watch your Process Explorer (a free download fro Microsoft-Sysinternals) and see where the CPU time is being spent.
Anti-Virus and Firewalls that hinder update checks (when on a network) will slow launches down.