Slow Speeds Over IPSEC VPN

So I will preface this post with saying I'm fairly new to Fortigate. So i'll just get right to my issue, We have an IPSEC VPN configured for our site to site traffic, the problem is we are getting at most 20 Mbps and it's fairly sporadic ranging from 1-20. We pay a company to manage our firewalls but they have worked for months with no success and I want to see if I can figure this out. 

All tests were performed using Iperf3 .

I did test connection over the internet between locations and I was testing between 90-100 Mbps which is closer to the speeds we pay for. Let me know what information I can provide. Any assistance is greatly appreciated.