That's 30% additional movement speed IF you manage to just build 100 AP as a support. Either you're fuckin snowballing off your ass, or you manage to build a singular AP item running a glass-cannon AP rune page. Which at this point, on Sona, will rarely ever work unless your opponent actually let's you win.
So basically, you have a 3 second 13% self ms buff and a 1.5 second 10% ms buff to allies. In lane, that means you're giving a singular person 10% movement speed, +1% for that 30 AP you maybe have.
Assuming a base ms on the ally of 340:
11% ms buff will equate to a raw 37.5 ms.
Boots give 25 flat ms, which are upgraded to give at least 45 ms.
Kayle gives a 17% MS + Heal at Rank 1 (30% base at Rank 5) coupled with a 7% AP scaling.
Bard Shrines offer a decaying 50% ms buff for the same duration as Sona, while also healing.
Janna's passive gives 8% while running to her.
Karma's shield grants 40% Movement Speed at Rank 1 with a shield.
Nunu gives an 8% MS buff with a 25% Attack Speed buff that lasts for -12 seconds-.
Lulu grants a 30% MS buff for 3-5 seconds that also scales with 10% AP.
Hell, Nami's abilities on allies will passively grant them 40 flat ms for 1.5 seconds with a 10% AP scaling.
Sona's E is probably one of the absolute worst ms buffs an ally can possibly want. Even non-supports do her job better, and in laning, the base values of other supports that could fit her play-style just do it better and often provide better CC, damage, or healing/shielding overall.