Counterspell at lower level spell slot?

Spell slots are a staple of Dungeons and Dragons for casting magic However, the DMG

spell he desires Drawn magic begins as an idea ; the caster chooses the slot during his preparation , but those he leaves empty can not be filled

spell slot slot , 15 , 17 shafman sike slot , slote shale , 17 sike spell spelder spell , speal ; see spelck spice spick and span shool , 17

spellcast slot How To Calculate Multiclass Spell Slots Multiclass characters determine the spells they have available and can prepare as normal for each