Just to make it more clear here. I currently have a personal Reserve (since 04/2015) and will have a business Platinum (since 06/2015).

In 2015, in my personal Reserve card, I will get a total of 40kMQM after $
60k spendings.
I can also get a total of 30k MQM from a business Platinum card after
another $50k spending.
This is already a total of $70k MQM! I only need another 5k to reach
Platinum!

Starting 2016, I can get 30k MQM from personal Reserve ($60k spending) and
20k MQM from business Platinum (50k spending).
This will be 50k MQM total in my 2016 account.

This seems very promising! Is it correct?

You're mostly correct. If before 12/31/2015, you spend $60,000 on your reserve card you will earn both bonuses. (One at 30k in spending and one at 60k in spending). The bonuses from the reserve card are 15k MQMs and 15k RDMs (redeemable miles) each bonus.

If before 12/31/2015, you spend $50,000 on your Delta Business Platinum card, you'll receive both bonuses. (One at 25k in spending and one at 30k in spending). The bonuses from the Platinum card are 10k MQMs and 10k RDMs each bonus.

As a side note, in one year you can upgrade the delta business platinum to a delta business reserve after you have met the 50k threshold, spend another 60k and get both Reserve bonuses too. (Apparently this works if you meet the reserve thresholds and then downgrade to the platinum and make those thresholds too).

I think your numbers might have been off from the one-time sign up bonuses. So you are correct.

Thank you! It seems to me that this is a strategy for Delta to make Frequent flyers to keep their spendings on DL credit cards!

My only question is can you not do $60k on your Business card instead of $50k and upgrade to the Reserve? The additional 10k MQM (and RDM) would be worth the higher Reserve annual fee in my opinion, unless you really can't get that extra $10k in spend.