Response times running on windows 10 XAMPP server

I think I may have simpleinvoices installed incorrectly and I’m seeking some advice. The system is loaded on my dev server which has typical response times for the web apps I develop. i.e. sub-second.
When I access simpleinvoices here are some typical timings
Open index.php – 15 seconds
Open Invoices screen – 5 seconds, them another 10 seconds to show the invoice grid.
New invoice button – 5 seconds to display blank invoice.

These sort of timings are the same across the system. I have about 100 invoices on the system.

Any guidance appreciated.
Thanks
Malcolm