Speed test through the modem gives proper results. Connect a Fortinet 110c IPsec VPN and speed is tremendously slow

Enable UTM feature only for outside to inside communication policies.
Avoid permit ip any any policies on outside.

Just a wild hairy guess.. maybe UTM is turned on in two devices and only necessary at the router.

Not all routers will pass all types of VPN successfully. My last D-Link router would pass a PPTP VPN with no problem, but completely choked on any attempt to pass an IPSEC VPN.
Since you never specified what model router you have, it's difficult to diagnose your problem beyond that observation.
Try a different brand or model of router and see if you get better results. Sad to say, I have found that the low-end routers work fine with completely vanilla networks, but they are very prone to annoying surprises like this when you try anything beyond what the average home user would try.

Real Apple Certified Experts might help you for free - http://bit.ly/2oONirp

as you told me that all the ports are open so in that case you can get in touch with your ISP and ask them to enable IPPASSTHROUGH on your office laptop.

The "Virtual Server" setting is designed to give the general public access to a network resrouce (web/ftp/media server) on your internal network. If your the VPN concentrator is external to your network (meaning you'll have to use the internet to connect to it), then you won't need to define a virtual server on the DI-624.

You'll just need to enable the IPSEC and PPTP VPN Passthrough which it sounds like you've already done this. I've run into some ISP's that block VPN connections out of their network. If you have the ability, try to directly connect your laptop into your cable/DSL modem in place of your router and see if you can make a VPN connection, if not contact your ISP, if you can then verify you enabled the VPN passthroughs because your router is blocking them.

GIve it a shot and let us know your results.

I'll need to know what router you're using, make and model, for more specific help, but sometimes there is an option for IPSec passthrough. For example, on my Linksys Wireless Router WRT54G, there is a set of buttons under Security/VPN that are entitled IPSec Passthrough, PPTP Passthrough, and L2TP Passthrough. Since I don't know what router you're using, I can't tell you wether or not your router supports such functions or not, but if it does, you need to enable them.

You'll want to enable the VPN transparency. In the router's administrative web interface, click the Security Tab, then the VPN Passthrough sub-tab. Cisco VPN's usually use IPSEC, so enable the IPSEC Pass-through and click "Save Settings". If this doesn't work enable the PPTP Pass-through as well and give that a shot.

Hi,
Please see the specicification, also check with you company
IT Admin, to release it to the Max speed or to check the
net work cable, may be too long, also Test the cable with a Data Test meter and conform the data quality. Or change the port from main router.
Otherwise change the whole networking router.

Regards

login to the router and check these things
IPSec Passthrough: Enable Disable               PPTP Passthrough: Enable Disable               L2TP Passthrough: Enable Disable