Hi roman,
The reason you are seeing the small amount of coins is because of the mining “slow start”
New Alpha Release: Mining Slow Start - Electric Coin Company
This means that for the first 20,000 blocks there will be a maximum of 12.5 ZEC issued per block. The ZEC issuance curve will ramp up over the 20,000 blocks to the full 12.5 ZEC and the difficulty algorithm will be adjusted as needed. This Slow Start is to prevent “insta-mining” and “fastmining” in the early days of the 1.0 launch and to allow the Zcash team to adjust the ZEC/time algorithm.
Also: The block interval is 2.5mins. So 12.5 ZEC every 2.5min is 50 ZEC every 10min.
Also you may be experiencing confirmation and connection difficulty due to the current DoS on the Testnet: