Slow speed in China is almost always caused by bad peering out of China mainland, trans-pacific fiber congestios and by the GFW throttling of VPN connections.
We suggest to use OpenVPN XOR, 256-bit and ECC as well as PPTP and L2TP/IPsec and try different server locations and different ports. Those in US West, Japan, Hong Kong, Singapore and Australia have better peering than others. European servers will always be slower and have greater latency due to non-existing direct peering between EU and China (to reach EU servers, the connection will go over Pacific, US, Atlantic). We also highly encourage you to check our Secureproxy extension for Google Chrome and Firefox, as it is very fast in China (most of the times faster than classic VPNs).
Also run a DNS leak test on https://www.dnsleaktest.com and see if it reports your ISP servers. In case it does, you will need to fix the DNS leak