What best speed burn MDisc DVDs?
 

1) What is the best speed to burn the mdisc verbatim DVD and have few burning errors and the disc last for many years?

2) Friend Lordsmurf said that my dvds (mdisc verbatim dvd) should last between 10-15 years regardless of my storage conditions, I believe that this count starts after burning the disc and not the manufacture of it, after 15 years the disc is disposable to throw in the trash the burned discs and the remaining not burning discs?

Half speed under = 12x burn for 16x media. 8x or slower as needed, if burner/media does not allow 12x.
No media is rated over 16x.
Same for all DVD media.

In 10-15 years, just migrate content to the then-current media of the day. Go ahead and retain old DVDs as yet another copy that exists. My old DVDs are in boxes in a closet now, and I use 2x HDD as my main storage. The DVDs are just the backup. When HDD gets bigger, I'll migrate again, put old HDDs in box. That's already happened. My DVDs are 10-20 older than yours. Still mostly fine, but only 1 of many backups.

1) In my DVD Mdisc Verbatim is written 4x and in my DVD-R Verbatim AZO is written 16x, which speed is the best for them and which free software burns to use for being the best?

2) In total I own the burned mdisc and verbatim dvds and the mdisc and verbatim azo dvds not burned (In pin) after 15 years all of them burned and unburned (in pin) will be discarded bad and throw in the trash and buy new optical discs?

3) Is it possible to store the discs in big plastic boxes or another container to protect from moisture and prolong the life of the discs for more than 15 years?

Write a 4x disc at 4x.
The 16x at 12x, 8x, or 4x. 12x best, then 8, then 4 last choice.

I see no reason to trash a good disc simply because it might be aging, but whatever. I've already explained this to you, not doing it again.

No.

If I put the disc inside a closed plastic box and inside the box put silica gel will this disk always be stored with low humidity?

good old disc to burn it will it be with many errors of burn?