Please be aware I am not familiar with this family personally, just did the research and have some information that may help you. Cites are included for each finding.
I was not able to find a Susan Lathrop b. 1815 to Zephaniah Lathrop.
Susan PECK however was born in 1815 and married Charles Henry Lathrop SR
The following is a cite from the marriage of their daughter, Jennie Lathrop.
"New York, Marriages, 1686-1980," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/F6WM-1G3 : accessed 26 Dec 2013), Geo W Clark and Jennie Lathrop, 22 Dec 1873
Right age, right location, but did not have a child named Susan:
Zephaniah Lathrop 1792
Born in Hawley Massachusets with residence in Oneida, New York.
Had six children: Henry Lathrop 1819
Rachel W Lathrop 1821
Joseph Lathrop 1823-1833
Solon F Lathrop 1827
Rosamond Olivia Lathrop 1830
Hope this helps, have a nice day.