At the end of the birthday celebrations of 15 years o2 they currently give (via the Mein o2 app) to every customer with o2 free or basic tariff 15GB for a month, but certainly some customers will also have enviously looked at the 15GB tariff it until recently still for 29.99 € gave.
Now, where the celebration is almost over, you do not have to be so envious, because the data volumes were drilled at the o2 free tariffs powerful except in the cheapest o2 Free S tariff. For Free M there are now 10GB instead of 2GB, for Free L 20GB instead of 4GB and for Free XL 25GB instead of 8GB. The last two are also 5 euros cheaper.
It thus clearly looks as if o2 had so good experiences with their anniversary star that they can now start an overdue price round with LTE tariffs with usable data volume.
PS: If you as an o2 customer somehow is not in the temporal proximity of a tariff change, can be a somewhat complicated procedure at least for the next two months in each case a 2GB extra volume over an action with computer picture.