see the below link
https://kc.mcafee.com/corporate/index?page=answerlink&url=0bc97397072bd71a8a439b 60a92c8cb6bcf890c2e2ab256f72a4f0ef40b3b41bd3368e5429e205303fdf486fa524750dede330 5e7647375cec628590fe5839278b481845b7219d35295bb075cc8aaf5f357b49dcda73a6ae4c367f abcd3e895a67cd7a70d9a0d8da039f7cccd47ddd1733ab7fd6068092926f935eab22de7986cc753f c47e56c886&answerid=16777241&searchid=1301175896557
The only thing I notice is that your DB is quite large for 7500 clients... I would recommend identifying what is taking up so much space and, if it's something like events (it usually is) then think about removing old events that you no longer need to keep.
The upgrade process from 4 to 4.5 needs to change the format of the events that are stored in the DB, so a large number of events means that the upgrade will take a long time. Removing events that are not needed will speed up the process considerably
And keep in mind that all your automatic responses (except RSD resonses) are lost during the upgrade - so a documentation would be good