I have :
First WAN port connected to Internet : RX 16 Mbit/s, TX 1Mbit/s
Second WAN port connected to Internet : RX 16 Mbit/s, TX 1Mbit/s

Load balancing mode is ON (According to line speed).
Also through 16-ports Switch connected 11 computer.
Question:
Whether there will be a common capacity of two WAN ports are 32 Mbit/s for download and 2Mbits for Upload simultaneously ?[/b]

The max throughput of the 2910 series is around 15-20 mbps if you look at this table:
http://draytek.co.uk/products/comparison.html
The firewall throughput is the relevant one, you'd need to go with something faster to get full capacity. That is assuming at both lines are connecting at 16Mbps, usually ADSL2+ speeds are lower than that depending on the distance from the telephone exchange.

I think he was asking not about throughput but whether the two feeds would aggregate, which they won't.