Actually, if you look at what is not said in DN 15, you might notice that this not-said makes allowance for name to be present without form.
It was said: ‘With mentality-materiality as condition there is contact.’ How that is so, Ānanda, should be understood in this way: If those qualities, traits, signs, and indicators through which there is a description of the mental body were all absent, would designation-contact be discerned in the material body?”
“Certainly not, venerable sir.”
“If those qualities, traits, signs, and indicators through which there is a description of the material body were all absent, would impingement-contact be discerned in the mental body?”
“Certainly not, venerable sir.”
“If those qualities, traits, signs, and indicators through which there is a description of the mental body and the material body were all absent, would either designation-contact or impingement-contact be discerned?”
“Certainly not, venerable sir.”
“If those qualities, traits, signs, and indicators through which there is a description of mentality-materiality were all absent, would contact be discerned?”
“Certainly not, venerable sir.”
“Therefore, Ānanda, this is the cause, source, origin, and condition for contact, namely, mentality-materiality.
(using BB’s translation, but I would advocate changing everything to “name” for his “mentality” and “form” for his "materiality, as in his more recent translations of the SN and AN)
Can you spot what is not said? The text does not discuss this -
If those qualities, traits, signs, and indicators through which there is a description of the form-group were all absent, would designation-contact be discerned in the name-group?
This clearly suggests that designation-contact with reference to the name-group is possible even in the total absence of form. How else can the formless attainments be accounted for?