Don't know if this is the cause.... but try changing the split tunnel ACL
Also, your nato should include the entire range of the ip local pool
no access-list VPN_splitTunnelAcl standard permit 192.168.10.0 255.255.255.0
no access-list VPN_splitTunnelAcl standard permit 192.168.1.0 255.255.255.0
access-list VPN_splitTunnelAcl extended permit 192.168.10.0 255.255.255.0 192.168.15.0 255.255.255.0
access-list inside_nat0_outbound extended permit ip 192.168.10.0 255.255.255.0 192.168.15.0 255.255.255.0