Interval recognition training is probably the worst way to get theory in your ear.
I went through interval recognition quizzes in my college theory class, and it was only daily drills that got past it.
I can think of 2 superior alternatives to interval drills:
#1 singing solfege
Singing solfedge is probably the best way to get intervals in your ear.
I used the Chrodbot app on my phone to generate a looping C major chord and practiced singing these while driving. The key is to reduce the number of notes you are trying to tackle, stick to variations of a single note combination, every day for a week. train yourself to sing just those 2 or 3 notes in various combinations:
Week 1: perfect fifth: Do So, So Do
Week 2: Add Mi for a major arpeggio: Do Mi So Mi Do, Mi Do Mi So Mi, So Do So Mi So
Week 3: Add Re
Week 4: Add La to build major pentatonic
...
#2 Learning the sound of common chord progressions
recognizing chord pressions is much easier than intervals in a vaccum
You can easily google common chord progressions and get examples of songs that use them
Most blues tunes follow I, IV, V
Listen to Stand by Me and then Every breath You Take (verse) : I vi IV V
Look up the Axis of Awesome's "Four chords" video
Look up the rhythm changes
I grew up listening to The Ramones....so I got I-IV-V progressions pretty good in a major key
