The most common and most likely answer to this crossword clue is the 15 letter word CHARACTERISTICS
C
H
A
R
A
C
T
E
R
I
S
T
I
C
S
More clues leading to the result CHARACTERISTICS
- Cleaner cries: attic is spoilt after one leaves marks
- Features East’s arch-critic misrepresented
- Ways odd fellow is a jerk? Stealing primarily
- Architect’s arch is unfortunately losing hospital marks
- Unusual care artist put into elegant, small features
- Architect’s car is dismantled for indicators
- Letters I almost stick inside properties
- Chap's a jerk with primarily sickening traits
- Archer's tactic is shattering marks
- Strict care is exercised to promote tea's qualities
Buddy explains!

The straight part
We know that "marks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marks = characteristics.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CHARACTERISTICS mean?
CHARACTERISTICS noun- A distinguishing feature of a person or thing.
- The integer part of a logarithm.
- The distinguishing features of a navigational light on a lighthouse etc by which it can be identified (colour, pattern of flashes etc.).
- For a given field or ring, a natural number that is either the smallest positive number n such that n instances of the multiplicative identity (1) summed together yield the additive identity (0) or, if no such number exists, the number 0.