Simple PPTP VPN solution became an nightmare .... I need an extra pair of eyes to tell me what's wrong

So I have a little group within our office, they have a LAN (LAN B), DHCP server and Internet access by UTM 9.404-5

LAN B = 10.10.15.0 - 255.255.0.0

I also have a larger LAN (LAN A) which is separated from LAN B via a Cisco switch and ACLs

LAN A = 10.10.10.0 - 255.0.0.0

I have a server (10.10.10.43))  in LAN A and I needed to grant access only to this server to LAN B, which I did by a port ACL in the switch.

Everything works fine, I can ping only the server 10.10.10.43 from LAN B, and of course this server is available to LAN A as well.

Now I need to allow some of these workers who are part of LAN B to have VPN.

I setup a SSL VPN first but I had problems with WIndows 10 users so I decided to use the simple "PPTP"

I configured and it with the following info

192.168.100.0 - 255.255.255.0

users, firewall rule and masquerading rules are enabled.

I can connect with no problem to the PPTP VPN

I can access to the internet, I can ping the UTM 10.10.15.1 and even www.google,com

But I can't ping the local servers in LAN B  for example 10.10.15.50 , but I can do it with no problem on any machine connected to the LAN B.

Now considering that LAN B and ip that I am getting from the VPN are not on the same network  (192.168.100.0)

Do I need to create routing rules? please advise

Thanks

Gaston