I have 0.015161 BTC in my Multibit HD wallet and now I want to move them all to Electrum wallet. So, how much fee to set for this transaction as a cheap way? And how long I must wait? The default value I see in Multibit HD is 0.0005 BTC/kb
https://bitcoinfees.21.co can give you an estimate of transaction fees based on the current network activity. It's recommended rate at the moment is 0.0026 BTC/kB to have a good chance of being included in the next block, but this changes often. Lower fees will take longer to confirm typically, but it's hard to be sure how long. At the rate multibit suggests, the website estimates it will take 4-28 blocks to be included, it estimates it could take up to 6 hours in the worst case.
At the current fee average on Bitcoin network you can easily set 2 satoshis per byte as tx fee if you are not in rush to have you transaction confirmed in the first block after you submit it.
Graphical info here: https://bitinfocharts.com/comparison/bitcoin-transactionfees.html#3m